1. Field of the Invention
The present invention relates generally to a servo circuit and, more particularly, is directed to a servo circuit suitable for use with an information signal reproducing apparatus such as a digital or analog VTR (video tape recorder) and so on.
2. Description of the Prior Art
Initially, a prior art digital VTR and its servo circuit will be described in brief.
In the digital VTR, if a video signal to be recorded is an NTSC video signal, each field of the video signal is separated into five portions and this separated video signal is recorded on a magnetic tape by two pairs of rotary magnetic heads, each being mounted with an angular spacing of 180.degree. therebetween, so as to form a pair of slant tracks for each 1/5 field.
Upon reproduction in a recording and reproducing apparatus, a segment pulse occurring every 1/5 field formed from a reference video signal generated from a video processor and a rotation detecting signal (having a period 1/5 of the field period) from a drum rotor are phase-compared and using the compared output therefrom, the rotation of drum motor is controlled to thereby provide a servo for the drum motor.
In such a conventional digital VTR, however, the servo is not sufficient and due to various unstable factors, upon reproduction digital data near the starting point of the slant track will frequently not be reproduced. As a result, a defect exists in that the dropped-out digital data can not be corrected for error in the vertical direction and hence error concealment is required. The drop-out of such reproduced digital data can not be detected the original reproduced picture but can be remarkably noticable in a reproduced picture based on a dubbed one.
Similarly in the prior art analog VTR, the servo is not satisfactory so that if a video signal on one slant track (one field) is reproduced while a part thereof is dropped out, the reproduced picture is deteriorated in quality.